In recent years, radiation detectors such as flat panel detectors (FPD), in which a radiation sensitive layer is positioned on a thin-film transistor (TFT) active matrix substrate and which may directly convert radiation such as X-rays into digital data, have been put into practical use. Radiographic imaging devices using these radiation detectors have the advantage that, compared to conventional radiographic imaging devices using X-ray film or imaging plates, images may be checked instantly, and fluoroscopy, which continuously images radiographic images (images moving images), may also be performed.
Various types of this kind of radiation detector have been proposed; for example, there is the indirect-conversion-type, in which the radiation is first converted into light by a CsI:Tl, GOS (Gd2O2S:Tb), or other scintillator and then the light, into which the radiation has been converted, is converted into electric charges by sensor portions such as photodiodes and the electric charges are stored. The radiographic imaging device reads out, as electrical signals, the electric charges that have been stored in the radiation detector, uses amplifiers to amplify the electrical signals that have been read out, and thereafter uses analog-to-digital (A/D) conversion sections to convert the electrical signals into digital data.
As a technology relating to this kind of radiation detector, in JP-A No. 2002-168806, there is disclosed a technology in which the radiation detector is positioned in such a way that radiation that has passed through a subject is made incident from the scintillator side, part of the side of the scintillator to which the radiation is irradiated is covered by a mask member comprising a material that does not pass through the radiation, and the degree of deterioration of the radiation detector is determined by comparing the dark current that is output from the photodiodes in the region covered by the mask member and the dark current that is output from the photodiodes in the region not covered by the mask member.
Further, in JP-A No. 2009-32854, there is described a radiation detector in which the sensor portions are formed by an organic photoelectric conversion material.